Note: Descriptions are shown in the official language in which they were submitted.
i333
APPARATUS AND METE~OD FOR COATING ELONG~TED STRIP
ARTI CLES
-
Background of the Invention
This invention relates to the coating of major
surfaces of elongated strip articles, such as sheet metal
strip and the like. More particularly, it relates to
apparatus and methods for continuously applying, to a
strip major surface, a layer of paint or other liquid
coating material.
By way of specific illustration, detailed reference
will be made herein to the coating of sheet metal in
greatly elongated strip form, as used for making siding
panels for cladding exterior building walls~ it being
understood, however, that the invention in its broader
aspec~s embraces the coating of other types of articles
and surfaces as well.
In the production of siding panels from metal strip,
at least one major surface of the strip is first given a
protective and decorative coating of paint, and the strip
is thereafter formed and cut into individual panels. ~s
described, for example, in U.S. patents No. 4,356,217 and
No. 4,411,218, it is known to perform strip coating on a
continuous line using a rigid coating head that defines an
elongated open-sided slot to which liquid coating material
(e.g. paint) is continuously supplied under pressure. The
strip is continuously advanced longitudinally past the
open side of the slot in a direction transverse to the
long dimension of the slot while a major surface ~f the
advancing article is maintained in facing proximate
~9.~
~" . " -.~
333
relation to the slot such that liquid coating material
from the slot is deposited in a layer on the advancing
strip surface. The thickness of this layer is dependent
on the spacing between the strip surface and the coating
head downstream of the slot; as shown in the
aforementioned patents, the head is provided with an
extended surface immediately adjacent the open side of
the slot, and this surface defines (with the strip
surface being coated) a metering orifice that determines
the thickness of paint coating carried on the strip away
from the slot. Typically, the strip advancing past the
slot is backed up by an axially fixed roll.
The aforementioned patents particularly describe
coating apparatus and procedures wherein the slot has
the form of a trench and the applied paint or like
coating has a striated or variegated appearance effected
by concurrent supply of at least two colors of paint to
the slot. The described apparatus and procedures,
however, may also be employed to apply a single-color
layer of paint.
In coating operations of this general type, desired
uniformity of coating thickness requires maintenance of
a metering orifice of invariant aperture; î.e., the
spacing between the coating head and the coated strip
surface, downstream of the slot, must remain constant
despite variations in thickness of the strip being
coated. Heretofore, it has been customary to control
the thickness of coating application by mechanically
fixing the position of the coating head surface relative
to the strip surface being coated. In order to
accommodate variations in strip thickness, in these
known systems, the entire coating assembly has been
mounted on small wheels that ride on the strip ahead of
the locality of coating application (i.e., ahead of the
slot). The use of such wheels has given rise to
:~2~333
-- 3 --
problems, especially in production of coatings of
uniform single color. It is found that the wheels make
visible marks that show through a single-color coating
applied over a primer coating, although these marks are
masked when the applied coating has a variegated or
striated pattern; since use of a primer coating is
generally desirable, and since the presence of such
marks detracts from the appearance and acceptability of
the coated product, the use of the wheels to maintain
uniform spacing is disadvantageous for monochromatic
coating applications~ Also, in an experimental run on a
strip-coating line employing the described wheels, bars
of varying thickness across the width of the sheet have
been observed; these bars are believed to have been
caused by the wheels, either through vibration or as a
result of the fact that the wheels must be spaced some
distance ahead of the slot. Again, the creation of
such bars detracts from desired coating uniformity.
Q~ lnYen~iQn
The present invention, in a first aspect, broadly
contemplates the provision of new and improved strip-
coating apparatus of the general type comprising a rigid
coating head defining an elongated, open-sided slot and
having an extended surface immediately adjacent the open
side of the slot; means for supplying liquid coating
material under pressure to the slot; and means for
longitudinally advancing a strip article successively
past the slot open side and the extended surface of the
head in a direction transverqe to the long dimension of
the slot while maintaining a major surface of the
article in ~acing proximate relation to the slot, so as
to constitute a moving wall substantially closing the
slot open ~ide, such that during operation with the
article advancing past the slot and liquid coating
_ 4 ~ 333
material supplied to the slot, the last-men~ioned
article major surface drags a layer of the coating
material from the slot. The apparatus of the invention
includes means for supporting the head while permitting
translational movement of the head relative to the
supporting means in a direction perpendicular to the
long dimension of the slot, and in this apparatus, the
strip-advancing means supports the strip, opposite the
slot, at a fixed distance from the head-supporting
means. As a particular feature of the invention, the
apparatus further includes means, acting between the
head-supporting means and the head, for continuously
exerting a load on the head to urge the head toward the
last-mentioned article major surface such that, during
operation as aforesaid, the head is pressed by the load-
exerting means against the deposited layer of coating
material to maintain the coating layer at a
predetermined constant thickness while that layer alone
holds the head entirely away from contact with the last-
mentioned article major surface.
Advantageously, the load-exerting means is
adjustable to vary the magnitude of the load, e.g. in
accordance with such factors as coating material
viscosity, strip speed, and desired coating thickness.
In illustrative and currently preferred embodiments, the
load-exerting means comprises at least one air cylinder,
and most preferably a plurality of air cylinders
positioned to act on the head at locations spaced along
the length of the slot. Also, in convenient or
preferred embodiments, the strip-advancing means
includes a roll having an axis parallel to the long
dimen ion of the slot and fixed in relation to the head-
supporting means, the roll further having a cylindrical
surface positioned closely adjacent the slot open side;
and the extended surface of the head is shaped and
- 5 - ~2~3~
positioned to approach progressively nearer to the
cylindrical roll surface in the direction of advance of
the strip article.
In a second aspect~ the invention contemplates the
provision of a method of coating a major surface of an
elongated strip article, comprising the steps of
supplying liquid coating material under pressure to an
elongated, open-sided slot defined in a rigid coating
head having an extended surface immediately adjacent the
open side of the slot, the head being supported for
translational movement in a direction perpendicular to
the long dimension of the slot, while continuously
longitudinally advancing a strip article successively
past the slot open side and the extended surface of the
head in a direction transverse to the long dimension of
the slot with a major surface of the article maintained
in facing proximate relation to the slot so as to
constitute a moving wall substantially closing the slot
open side~ such that the last-mentioned article major
surface drags a layer of the coating material from the
slot, and while continuously exerting a load on the head
to urge the head toward the-last-mentioned article major
surface such that the head is pressed by the load-
exerting means against the deposited layer of coating
material to maintain the coating layer at a
predetermined constant thickness while that layer alone
holds the head entirely away from contact with the last-
mentioned article major surface.
In the apparatus and method of the invention~ the
maintenance of a load on the coating head for control of
coating layer thickness enables the head to conform
positionally to variations in strip thickness (for
maintaining a constant metering orifice aperture)
without resort to wheels riding on the sheet; hence the
problems associated with such wheels are avoided. In
addition, the provision of the defined load-exerting
means or step improves accuracy and ease of set-up.
Further features and advantages of the invention
will be apparent from the detailed description
hereinbelow set forth, together with the accompanying
drawings.
e--c~i~ti-~-Q~-~he-D~awi~a~
Fig. 1 is a simplified, schematic elevational view
of coating apparatus embodying the present invention in
a particular form;
Fig. 2 is a plan view (to a smaller scale) of the
apparatus of Fig. l; and
Fig. 3 is an enlarged fragmentary sectional view of
a modified form of coating head, taken as along the line
3-3 of Fig. 2.
~,t a il~ d _~.c E~et iQn
The invention is illustrated in the drawings as
embodied in procedures and apparatus for coating sheet
metal strip to establish a uniform~ single-color paint
20 layer on a major surface of the strip before the strip
is formed and cut to produce siding panels. Such strip
is typically an elongated, flat sheet metal article
(having a length corresponding to the combined lengths
of a substantial number of panels, and a width
corresponding to the width of one or more panels), of a
gauge suitable for siding panels, and is usually coiled
for ease of handling.
In the coating apparatus schematically shown in
Figs. 1-2, metal strip 10 to be coated is continuously
advanced (by suitable and e.g. conventional strip-
advancing means) longitudinally parallel to its long
dimension from a coil (not sh~wn) around a back-up roll
14 rotatably supported (by ~tructure not shown) in an
_ 7 ~ 3~3
axially fixed position. At a locality at which the
strip is held against the back-up roll, paint is applied
to the outwardly facing major surface 17 of the strip
from a coating device 18, to establish on the strip
surface 17 a continuous layer or coating of the paint.
It will be understood that the major surface 17 of the
strip 10 may bear a previously applied undercoat or
primer coat of paint, and the opposite surface of the
strip may also be precoated. Beyond the roll 14~ the
strip is passed through an oven to cure the coating and
thereafter coiled again, e.g. on a driven rewind reel
(not shown) which, in such case, constitutes the means
for advancing the strip through the coating line; within
the oven (which is also not shown) the advanclns strip
is in catenary suspension, and the weight of the
suspended portion holds the strip against the back-up
roll 14. The direction of strip advance through the
coating line is indicated by arrow 21.
The coating device 18 includes a rigid coating head
comprising a metal block 22 having a flat or concavely
curved surface 24 spaced from the roll surface to define
therewith a gap through which the advancing strip 10
passes. As best seen in Fig. 2, the head 22 extends
over the entire width of the strip at a locality, in the
path of strip advance, at which the strip is held
again~t the surface of the roll 14.
Formed in the head 22 is an elongated slot 26 which
opens outwardly through the surface 24 of the head but
is otherwise fully enclosed by the head except for
paint-delivery apertures 28. This slot, in the
embodiment shown in Fig~ 1-3, is an axially rectilinear
cavity in the form of a trench having flat closed ends,
and a uniform cross-section throughout. It is oriented
with its long dimenslon transverse to the direction of
advance of the strip 10; very preferably, the long
-- 8 --
dimension of the slot is perpendicular to the direction
of strip advance and parallel to the axis of rotation of
the roll 14.
Extending within the head 22, in axially parallel
relation to the slot, is an elongated enclosed manifold
chamber 29 for containing liquid coating material
(paint) under pressure. Paint is supplied to the
manifold through one or more feed passages 30 formed in
the head 22, and is conducted therefrom to the slot 26
through the aforementioned apertures 28, which are
individually controlled by valves 31. In operation~
paint is continuously delivered from a container (not
shown) under pressure (by any suitable, e.g.
conventional, means, not shown, typically employing
15 hydrostatic pressure or a pump to provide the required
pressurized feed) through at least one of the passages
30 to the manifold at a rate sufficient to keep the
manifold entirely filled and to force the paint
therefrom under pressure through the apertures 28 to the
slot 26, so that the slot as well is continuously
entirely filled with paint under pressure. For uniform
monochromatic coating, a single color of paint is
supplied to the manifold, and all the valves 31 are
maintained at a constant setting (some at least being
open); however, the head 22 is also capable of use to
produce a striated or variegated coating of t~o or more
colors, by appropriate supply of such plural colors and
periodic opening and closing of different valves 31 to
vary the pattern as coating proceeds. In a broad sense,
the apparatus and method of the invention are equally
applicable to the production of single-color and multi-
color (patterned) coatings.
In the modified head structure 22' shown in Fig. 3,
the apertures 28 and valves 31 are omitted, and the slot
(designated 26') opens rearwardly along its full length
33;~
directly into the manifold 29'. This slot 26' is
narrower (in the direction of strip advance) than slot
26 of Figs. 1 and 2, being defined by parallel plane
walls extending from surface 24' to manifold 29', and
is, again, closed at its ends (not shown in Fig. 3). By
way of example, the width of slot 26' in the direction
of strip advance (vizo the width of the slot opening
through surface 24') may be 0.04 inch, and the length of
the slot (from surface 24' to manifold 29') may be 1/4
lo inch. This head is suitable for use in accordance with
the invention to apply a single-color paint coating to a
strip surface, the paint passing from manifold 29' to
the slot opening in surface 24' along the entire length
of the slot. Except for the differences just set forth,
the head 22' of Fig. 3 may be considered es~entially the
same as the head 22 of Figs. 1 and 2, and the following
de3cription of the invention, though particularly
addressed to the embodiment of ~igs. 1 and 2, is equally
applicable to a head of the form shown in Fig. 3.
As will be understood from the Eoregoing
description, the slot 26 has an open long side (viz. the
opening of the slot through surface 24) which extends,
transversely of the path of strip advance, from end to
end of the slot. The location and length of the open
slot side determine the position and width, on the
advancing strip, of the coating to be applied. That is
to say, the open long side of the slot has a length less
than or equal to the strip width, and is disposed for
register with that portion of the width of the ~trip
surface 17 which is to be coated, The back-up roll 14
supports the strip sur~ace 17 in proximate facing
relation to the open side of the slot as the strip
passes the slot, so that the surface 17 constitutes a
moving wall that closes the open slot side and enables
the slot to be maintained filled with paint.
- 10 ~ D63 ~ 3
The described arrangement of slot and strip results
in deposit of paint from the slot onto the strip surface
17 over the full width of the portion of the surface 17
that coincides with the open side of the slot, i.e. when
the slot is filled with liquid paint delivered through
the aperture 28. The deposited paint is carried out of
the slot as a coating on the advancing strip surface,
past the outlet edge of the open side of the slot and
through the gap between the surface 24 and the roll 14
beyond the slot. The downstream edge 32 of surface 24,
shown as a sharp discontinuity between the surface 24
and the upper end 33 of the head 22, extends across the
width of the deposited paint coating on the strip
surface 17 and, together with the surface 17, defines a
metering orifice that determines the thickness of paint
coating carried on the strip away from the head: as will
be understood, the spacing between the surface 17 and
edge 32 should be such as to constitute a gap providing
a desired wet thickness of paint coating on the surface
17, this wet thickness being less than the aperture of
the gap. The coated strip surface emerges from beneath
the head past edge 32. Preferably, the plane of end 33
forms an angle (opening upwardly toward the direction of
strip advance) of at least about 90 with the plane
tangent to the strip surface 17 at edge 32, for assured
avoidance of pick-up of paint from the emerging strip
onto the surface 33; in Fig. 1, this angle is shown as
greater than 90.
As illustrated in Fig. 1, the head 22 is preferably
so disposed that its slot, facing back-up roll 14, lies
in a near-horizontal plane containing the axis of
rotation of the back-up roll, and the coating line is so
arranged that the strip is held against the back-up roll
at this locality, which is thus the locality at which
paint is applied to the strip. It will be understood
that in continuous coating of strip, successive lengths
of strip are usually joined together (spliced) endwise
at a transverse seam which is thicker than the strip
gauge; when this seam passes between the head 22 and
roll 14, the head must be temporarily moved away from
the roll sufficiently to accommodate the thickness of
the seam. The disposition of the head shown in Fig. 1
facilitates this operation because paint in the slot,
when released by movement of the head away rom the
strip, falls clear of the strip surface rather than
falling on and fouling the qtrip surace as would occur
if the head were located above the strip.
The apparatus of the invention, in its illustrated
embodiment, includes a deck 40 having a flat upper
surface on which the head 22 rests, the head being thus
supported for translational (sliding) movement relative
to the deck in a generally horizontal direction (arrow
42) perpendicular to the long dimension of the slot 26,
i.eO toward and away from the roll 14. As best seen in
Figs. 1 and 2, a pair of vertically opening slots 44,
elongated horizontally in the direction of arrow 42, are
formed in the body of the head 22 rearwardly of the
manifold 29 at locations spaced along the length of the
head; a pair of bolts 46 respectively extend through
these slots and are threaded in the deck. The bolt
heads 46a overlie the top surface of the coating head 22
for preventing vertical movement of the head 22 relative
to the deck, while interference between the bolt shanks
46b and the side walls of the slots 44 prevents lateral
movement of the head 22 relative to the deck, but the
elonqation of the slots permits the head 22 to move in
the direction of arrow 42 through the full range of
operative head positions.
The deck 40 is mounted on a fixed frame 48 for
pivotal movement about a horizontal axis 50, so as to
enable the head 22, with the deck, to be swung upwardly
(e.g. by suitable pneumatic means, not shown~ from the
position illustrated in FigO 1 to a position removed
from the path of strip advance. An arm 52, fixedly
secured to the frame 48 and underlying the deck 40,
carries a screw 54 that projects upwardly from the arm
and bears against the lower surface of the deck 40, to
enable adjustment of the angular orientation of the head
22 in its operative position.
The frame 48 is fixed in position relative to the
axis of the roll 14, both the frame and the roll being
(for example) fixedly mounted in a common support
structure (not shown). Thus, the axis S0 is fixed in
position relative to the axis of the roll 14; and when
the deck 40 is in the operative position shown in Fig.
1, with the screw 54 set to provide a desired angular
orientation~ the roll 14 supports the advancing strip
10, opposite the slot 26, at a fixed distance from the
deck 40.
In accordance with the invention, and as a
particular feature thereof, the apparatus further
includes means acting between the deck-40 and the head
22 for continuously ~xerting a load on the head to urge
the head toward the facing major surface of the strip
10. This load-exerting means, in the illustrated
embodiment of the apparatus, comprises a pair of air
cylinders 56 fixedly secured to the deck 40 rearwardly
of the head 22. As shown, the cylinders 56 are secured
to rearwardly projecting ledge portions 58 of the deck,
respectively adjacent opposite extremities of the long
dimension of the slot 26. Each air cylinder includes a
piston having a shaft 60 which extends forwardly from
the cylinder, and through a guide block 62 mounted on
the deck 40, to bear against a rear surface of the head
22, Thus, actuation of the air cylinders (which may be
~633
-- 13 --
of a generally conventional character and accordingly
need not be described in detail~ causes the piston
shafts 60 to push the head 22 toward the surface 17 of
strip 10, i.e. t~ward the roll 14. As best seen in Fig.
2, the localities of engagement of the two air cylinder
piston shafts 50 with the head 22 are spaced
equidistantly from the extremities of the slot 26; in
the case of a very long head, a greater number of air
cylinders may be employed, and in such case, these
additional cylinders may be arranged to act on the head
at locations spaced along the slot long dimension.
The operation of the described apparatus, and the
performance of the method of the invention therewith,
may now be readily explained. With a strip 10 (e.g.
having a primer coating on surface 17) extending around
the roll 14 as shown in Fig. 1, and with the deck 40 in
the operative position also shown in Fig. 1, the
cylinders 56 are actuated to exert on the head 22 a
predetermined load urging the head against the str~p
surface 17. This load initially brings the edge 32 of
the head against the primer-coated strip surfaceO As
advance of the strip commences, and paint is supplied
under elevated pressure to the manifold and thence to
the slot 26 of the head 22, the fluid pressure of paint
forced into the space between the strip surface and the
head surface 24, in the direction of strip advance,
causes the head 22 to back off from contact with the
strlp surface. Thereby, a metering orifice is defined
between the head edge 32 and the strip surface 17, the
size (aperture~ of this orifice being determined (for
paint of a given viscosity) by the magnitude of the load
exerted by the cylinders 56.
It will be appreciated that the rate of paint flow
through the slot 26, and the fluid pressure of palnt
acting on the surface 24 in the gap beyond the slot, are
- 14 - ~25~3~3
primarily determined by drag forces of the strip rather
than by the supply pressure of paint in the manifold.
Thus, a small positive supply pressure (e.g. 5 p.s.i.)
is typically sufficient, and the aforementioned drag
forces, as the strip surface moves past the slot
opening, create a much higher fluid pressure between the
strip surface 17 and head surface 24.
As advance of the strip 10 continues, with
continuing supply of paint under pressure to the slot
26, a uniform layer of paint is deposited on the strip
surface. Throughout the operation, the cylinders 56
continuously maintain a load on the head 22, urging the
head toward the strip surface being coated, and this
load serves to maintain the aperture of the
aforementioned metering orifice constant, regardless of
local variations in strip thickness. In effect, the
head surface 24 floats on the layer of paint being
applied, and is maintained (by that layer alone)
entirely away rom contact with the strip surface while
coating proceeds. The invariant aperture of the
metering orifice, resulting from the described load on
the head, produces a paint coating of uniform thickness.
As will be appreciated9 in the described coating
operation, force is generated when the gap between the
strip surface and the head surface 24 converges. The
force generated depends on paint viscosity, strip speed,
width of the surface 24 downstream of the slot~ and, to
a lesser extent, on the angle of convergence, in a
manner consistent with principle~ of lubrication theory.
The load to be exerted on the head 22 by the cylinders
56 in any particular operation is determined by the
viscosity of the paint being applied, strip speed, and
the desired thickness of the coating; thus, at the
outset of a given coating operation, the cylinders 56
are adjusted to provide the particular load required for
that specific operation.
~25~;~33
- 15 -
For optimum performance, the configuration and
dimensions of the head surface 24 are also selected with
reference to the factors of viscosity and desired
coating thickness. Stated in general, application of a
relatively thin film or layer of a high viscosity
coating is best performed with a head in which the
dimension of surface 24 between the slot and edge 32 is
narrow, while for application of relatively thick films
of low viscosity coatings, a relatively wide surface 24
is preferred. Heads with a dimension of surface 24
~between the slot and edge 32~ of 1 mm to 19 mm have
been found suitable. It is important that the head 22
provide an extended surface 24 (as distinguished from a
sharp edge) on the outlet or downstream side of the slot
26, in order to achieve the above-described floating
action, i.e. in order that the head, under load, will
ride on the applied liquid coating layer and be held by
that layer away from contact with the subjacent strip
surface.
It is convenient to provide the head with two
differently dimensioned portions of surface 24
respectively disposed on opposite sides of the slot 26,
to enable the same head to be employed for application
of different coatings (as to which different downstream
dimensions of surface 24 are desired) by simply
inverting the head in the apparatus.
As indicated in Fig. 1, the gap defined between the
surface 24 and the strip surface being coated, beyond
the slot 26, should be convergent in the direction of
strip advance; i.e., the surface 24, in its extent
between the slot and the edge 32, should be shaped and
positioned to approach progressively nearer to the
cylindrical surface of the roll 14 in the direction of
advance of the strip 10. It has been found that
regardless of the width of surface 24, the best results
16 ~ 333
are obtained in the present coating method when the
difference in strip-head clearance between the outlet
edge of the slot 26 and the edge 32 is in the range of
about 5-150 microns, and preferably about 10-75 microns.
This preferred arrangement necessitates that the surface
24 be curved to conform to the curvature of roll 14 when
the surface 24 is of large width (dimension between the
slot and edge 32).
While the air cylinders illustrated in the drawings
and described above represent a currently preferred
means for exerting a oontinuous (yet adjustable or
selectable) load on the head 22, other arrangements may
also be employed. For example, the load could be
exerted by springs acting under compression between the
rear surface of the head 22 and structure fixed to the
deck 40, such springs being arranged in known manner to
enable variation in their degree of compression for
adjusting the magnitude of the exerted load.
Stated more generally, the purpose of the load-
exerting means is to exert, on the applied liquidcoating layer between the coating head 22 and the strip
surface 17, a load which is maintained essentially
constant across the full width of the strip and
throughout the duration of a ~iven coating operation,
thereby to achieve the desired constant and uniform
aperture of the metering orifice defined between edge 32
and the strip surface 17. In many instances, this
objective is adequately achieved by simply operating the
air cylinders 56 (in the illustrated embodiments of the
invention) to exert a constant load of preselected
magnitude on the head 22, balanced between the ends of
the slot, for the duration of a given coating operation.
In other cases, it may be preferable ~for example) to
vary the supplied load along the length of the trench,
viz. to exert a load which tat any given point in time)
- 17 ~ 33
may be nonuniform over the trench long dimension,
fluctuating in accordance with nonuniformities in the
advancing strip across the width of the strip, thereby
to maintain a constant load on the applied paint layer
across the strip width by compensating for these
nonuniformities; and the coating head itself may be made
somewhat flexible (in the direction transverse to the
strip) to facilitate compensation for such
nonuniformities, all within the broad contemplation of
the invention.
It is to be understood that the invention is not
limited to the features and embodiments hereinabove
specifically set forth but may be carried out in other
ways without departure from its spirit.
